Time domain
reflectometers are often compared and
referred to as 'radar' devices for
cables as they generate pulses and then
measure the reflections that may follow.
In the case of cables, these reflections
come from impedance changes along the
length of the cable.

The impedance changes
can be caused by normal parts of cable
such as ends, taps, joints/splices, but
TDRs are also able to locate cable
faults, such as open or shorts. In
addition, less subtle, but equally as
important abnormalities in the cable
system, such as concentric neutral
corrosion or degradation, moisture
ingress can be detected.